The defibrillator is a physiotherapy instrument that discharges a capacitor through the chest of the patient (external defibrillation) or directly through the expired heart (internal defibrillation) to bring the random activity of the fibrillating heart to a standstill and allow the organ to resume its normal rhythmic pulsations. The capacitor is discharged through a pair of external paddle electrodes placed against the patient's chest or a pair of internal electrode paddles placed directly on the heart. To sufficiently shock the patient's heart and return it to its normal rhythm, discharge voltages as high as several thousand volts are employed.
U.S. Pat. No. 3,389,703 discloses a defibrillator electrode suitable for performing defibrillation. The electrode comprises a shallow circular dish with a handle extending therefrom. The surface of the dish which contacts the patient is convex. Smaller versions of electrodes similar to the one shown in U.S. Pat. No. 3,389,703 have flat contact surfaces. Other types of defibrillator electrodes have disk-like shapes and radially attached insulated handles.
It is extremely important that the defibrillator be checked to ensure that it is functioning properly before the electrodes are placed on the patient and the capacitor is discharged. The wires connecting the defibrillator to the electrodes are typically constructed of carbon fiber which are prone to breakage. Currently, a defibrillator charge tester is employed to detect that the electrodes are charged.
FIGS. 1, 2 and 4 shows one such prior art charge tester and FIGS. 3 and 5 illustrates how it is employed. FIG. 1 is a top perspective view of the entire tester and FIG. 4 is a bottom perspective view of a portion of the tester. FIG. 2 shows the charge testing circuit disposed inside the tester. FIG. 3 is a perspective view showing how the tester contacts the defibrillator electrodes and FIG. 5 is a sectional view showing the tester/electrode contact.
FIG. 1 is a top perspective view of the prior art tester 100. The tester 100 consists of a generally Y-shaped flattened nonconductive hollow plastic shell 101. The Y-shaped shell 101 is defined by identical tines or prongs 102, 104 and a handle portion 106. Each prong 102 and 104 has a rounded distal end 108 and a proximal end 110. A pointed conductive pin or contact member 112 extends from the distal ends 108 of each of the prongs 102 and 104. The handle portion 106 includes ridges 114 for assisting the operator in gripping the tester 100. The mid-section of the top side of handle portion 106 has a cut-out covered by a translucent window 116. The contact members 112 actually extend through the shell 101 and thus terminate inside of the shell 101, as best shown in prior art FIG. 2.
FIG. 2 shows charge testing circuit 118 superimposed over the tester 100 with the components of the testing circuit 118 in their approximate locations with respect to the parts of the shell 101. It should be understood that all portions of the testing circuit 118, except for the protruding portion of the contact members 112, are disposed inside the shell 101.
The testing circuit 118 is a series connected path consisting of the two contact members 112, a resistor 120 and a lamp 122. One end of the resistor 120 is connected by wire 124 to the contact member 112 associated with the prong 104. The other end of the resistor is connected to one terminal end of the lamp 122. The other terminal end of the lamp 122 is connected by wire 126 to the contact member 112 associated with the prong 102. The lamp 122 is a glass neon bulb rated such that it will turn on when connected to 110 volts AC and will withstand instantaneous voltages of at least 550 V AC. The resistor 120 is 470 K.OMEGA. and rated for 1/4 W. The lamp 122 is positioned inside the shell 101 so that it is aligned with the translucent window 116 shown in FIG. 1.
FIG. 3 is a perspective view showing how the prior art tester 100 contacts defibrillator electrodes 128 and 130 after the defibrillator's discharge capacitor is indicated as being charged. The electrode 128 has a patient contact surface (dish surface) 132 and the electrode 130 has a patient contact surface (dish surface) 134. The tester 100 and electrodes 128 and 130 are positioned so that the contact member 112 associated with the prong 102 touches the contact surface 132 of the electrode 128 while the contact member 112 associated with the prong 104 touches the contact surface 134 of the electrode 130. If the capacitor is charged, the voltage across the contact members 112 will cause the lamp 122 to glow. The glowing lamp 122 will be visible to an operator through the translucent window 122.
A typical testing routine involves setting the defibrillator to output a relatively small amount of energy, such as about 2-5 joules, and touching the contact members of the tester 100 to the respective contact surfaces of the electrodes 128 and 130. If the lamp 122 glows, the tester 100 is removed, the defibrillator is turned up to its working setting and the electrodes 128, 130 are placed on a patient for discharge. In one type of defibrillator employed today, the working setting is about 100 joules for internal defibrillation and up to about 300 joules for external defibrillation. The testing routine is conducted at much lower energy levels because small defects in the carbon fiber wires connecting the defibrillator to the electrodes are more readily detected at such lower levels. Testing at lower energy levels is also safer. At higher energy levels, the voltage will spark or jump across the electrodes 128, 130 as the tester's contact members are brought in close proximity thereto.
The prior art tester 100 suffers from numerous disadvantages. One disadvantage is that each of the contact members 112 terminate in a pointed end. A pointed end easily scratches electrode contact surfaces. Also, pointed ends make point contact with the electrode contact surfaces. Point contact is disadvantageous because it requires relatively delicate maneuvering to ensure that appropriate contact is made and because it presents a relatively small surface area for contact. Since the tester 100 is usually employed in emergency or highly stressful conditions, the need to employ delicate maneuvering while conducting the test is not desirable. The relatively small contact surface, illustrated in FIGS. 4 and 5, is not desirable in view of the extremely high voltage levels associated with defibrillators. Furthermore, since resistance at the contact area is inversely related to the contact surface area, a small surface area will result in a high resistance. Preferably, resistance at the contact area should be as low as possible.
FIG. 4 shows a bottom perspective view of the prongs 102 and 104 of the prior art tester 100. As clearly shown in this view, the distal ends of the pointed conductive contact members 112 have very little surface area. The contact members 112 in this prior art tester 100 have an outer diameter d.sub.1 of about 2 mm. Thus, the maximum surface area of the distal end of the contact member 112 is about .pi.(2 mm/2).sup.2 or about 3.14 sq. mm. However, since the ends of the contact members 112 are rounded to a point, the actual surface area of the distal end is much less than this value.
FIG. 5 is a sectional view of the prior art tester 100 showing the contact member 112 of the prong 102 in contact with the contact surface 132 of the electrode 128.
Another disadvantage of the prior art tester 100 is that it is reusable. Although reusability would normally be a desirable feature, reusability in this instance creates potential medical problems. It is essential that the tester 100 be properly sterilized before use. Accordingly, the tester 100 is sterilized by the supplier and shipped in sealed plastic wrappers which are removed immediately before use. After use, the tester 100 is obviously not sterilized anymore. Furthermore, if the same patient is given repeated shocks, the tester 100 will touch electrodes which have directly contacted the patient, assuming that the same tester 100 is used with each patient episode. Thus, the tester 100 could potentially harbor infectious matter which might contaminate the next patient if the same tester 100 is reused. Currently, there is no fail-safe way to ensure that medical facilities do not reuse the tester 100.
Thus, there is still a need for a defibrillator charge tester which is easy to maneuver, which makes improved contact with electrodes and which cannot be inadvertently reused. The present invention fills that need.